The invention relates to tagged scale-inhibiting polymers, to compositions comprising said polymers, and to a method for preventing or controlling scale formation in systems comprising said fluids.
Scale formation is a problem to be addressed in most water containing systems. Scale formation can occur when the physical environment of the water changes to result in the solubility limit of certain compounds being exceeded. For example, changes to the pH, temperature, pressure or composition of the water can all result in the deposition of scale. The most problematic scales are metal sulfates and carbonates, especially Barium sulfates in oilfield production. Scale formation can cause many problems, for example it can impair heat-transfer in boilers and condensers, and may block pipe-work. In oil recovery and, more importantly, in secondary oil recovery (where water is injected into an oil well in order to displace the crude oil and repressurize the formation), scale formation may cause blockage of pipe work and the pores in the oil-bearing strata, thus reducing or even preventing the flow of oil.
In order to address scale formation, scale-inhibiting chemicals, for example polymers, phosphonates, polyphosphates are known. Treatment levels vary from system to system and typically range from less than 1 ppm up to several hundreds of ppm. Scale inhibiting chemicals are used in a wide range of water utilizing industrial applications, for example, oil industry applications, including secondary oil production, cooling towers, boilers, thermal desalination plants, membrane separation processes, mineral ore extraction, paper pulping, paper manufacture and geothermal power production facilities, to name but a few.
In most of these applications, the scale inhibiting chemical can be dosed directly into the system using a simple chemical dosing system. For secondary oil recovery, the scale-inhibiting chemical can be applied to oil bearing formations by means of “squeeze treatment”. Squeeze treatment involves pumping scale inhibitor into an oil production well so that the inhibitor enters the formation rock and is retained there. When the well is put back into production, the produced fluids are treated by the scale inhibitor which leaches out of the formation rock. Thus the scale inhibitor is released in the fluid displacing the oil. The scale inhibitor may be applied in an aqueous or non-aqueous medium, as a solution, an emulsion or as an encapsulated product. The scale inhibiting chemical can also be used in topside oilfield processes.
The objective is to prevent or control the scale formation in systems wherein the fluid is used.
Scale formation is only controlled if the scale inhibiting chemical is present at a treatment level within the product's defined effective range. However, most water systems needing scale control treatment have liquid losses which remove treated water from the system. Also, scale inhibitor may be lost through, for example by adsorption or degradation. Hence, there is a need to replenish the scale inhibitor to replace this loss. Additionally, with squeeze treatment, the concentration of the scale inhibitor in the produced fluids will diminish over time till a repeat “re-squeeze” operation is necessary. The consequences of scaling is often catastrophic in this application and so it is most important to avoid scale. Overall, it can be seen that the concentration of scale inhibitor in the treated fluids is very important and chemical analysis of scale control chemicals, particularly polymers, has always been difficult at ppm levels. The problem of analysis has recently become more important in subsea tiebacks used in oil production, because, typically, subsea completions utilize several individual wells where the fluids flowing from these wells are combined on the seabed and the combined fluids are piped to the nearest production platform which may be several tens of miles away. In this case it would be necessary to treat the individual wells with scale control chemicals which can be individually analyzed.
Hence, a good analytical method for the scale inhibitor chemical is required for at least one of the following reasons:                To ensure that the concentration of scale inhibitor chemical does riot fall outside of the effective range,        To help optimize dose rates, and/or        To avoid stopping the production for re-squeezing whereas it was not actually needed.        
As measuring the concentration of scale inhibitor chemicals, particularly polymers, is difficult because of the low concentration (up to a few hundred ppm), it has been suggested to use tagged, or “labeled” polymers, having groups that are easily detectable. Numerous references teach of the generation of tagged scale-inhibiting polymers, and methods for measuring the amount thereof.
Reference EP 157465 describes a copolymer comprising a group to be reacted with a diazonium salt for measuring the amount thereof by colorimetry.
Reference WO 01/44403 describes a copolymer comprising a pyrene-derived group, for measuring the amount thereof by fluorometry.
The invention concerns other tagged polymers that have advantages over the prior art. The polymers are especially suitable for use in oil recovery systems, but are also applicable for use in any water utilizing system where detection of scale control additives would be beneficial, for example boilers, cooling towers, mineral ore extraction paper pulping, paper manufacture, geothermal power production facilities, membrane separation processes and thermal desalination plants. The tags and the tagged polymers have a good resistance to salts (brine) and temperature. They are detectable even in the presence of compounds that are comprised in the fluid, such as antioxidants, or non recovered oil.